Extruded polystyrene (XPS) foams have been used for some time in sound and insulation applications. The foams are formed by extruding continuously a heated plastic resin containing a blowing agent through a die, which upon exiting the die expands under, for example, steam or vacuum. Generally, these foams have been limited to applications only requiring simple shapes or complex shapes with a thin thickness. For example, simple shapes include toys that are die cut out of a board that are essentially flat including puzzles and imitation badges. Other more complex shapes, generally, have been made by thermoforming. Thermoforming, however, commercially has been limited to shapes using thin XPS sheets such as milk crates. This is due to the long times necessary to heat and cool the foam to enable molding the foam.
More complex shapes of polystyrene have, generally, been formed using partially foamed beads of polystyrene that still contain a blowing agent and air diffused therein as a result of aging of the foam from ½ to 6 days. The beads are then placed in a mold and heated sufficiently to expand the beads further such that they fill in the mold and weld to each other. Polystyrenes made this way are typically referred to as expanded polystyrene (EPS). Examples of EPS shapes include, coffee cups, cushioned packaging shapes (e.g., shapes that provide cushioning to shipped articles), and bike helmets. This method of forming polystyrene shapes suffers from a complex method involving multiple heating and cooling steps and costly molds that need to be heated and cooled.
Other 3-dimensional shapes of polystyrene foams have been made by dye cutting flat shapes and laminating them together as described in U.S. Pat. No. 6,129,969. This method suffers from multiple steps to fashion the shaped article.
Finally, polystyrenes foam properties have been modified by uniformly crushing the foam one or more times. This elasticizing/flexibilization allows for the foam to bounce back after being impacted or bent further without being broken. For extruded foams, the crushing is typically done by roll presses. Examples of such crushing are described in U.S. Pat. Nos. 3,445,406; 4,510,268; 5,114,656; 5,520,873; and 5,718,968.
Accordingly, it would be desirable to provide a forming method for extruded polystyrene that is able to quickly shape complex extruded polystyrene shaped articles and in particular thicker shaped foam articles (e.g., greater than about a couple of millimeters thick).